rickjansen wrote:

@Dillen: Saw a post regarding the prescaler in the archived forum: /forum/general-discussion-and-questions/beoplay-e8-earbuds asking wether the u264b and u664b prescalers are  equivalent, Well, my Beomaster 8000 has a u664b, so the answer is yes.

rick

So that you have one that works confirms that they are identical?
What about the handful or more U664Bs that I've had that didn't work, where U264Bs did - doesn't that confirm that it's something that cannot be guaranteed?

And yes, during production it turned out, that some processors simply couldn't keep count at the higher frequency, so to keep it safe an
additional divider was introduced and the CPUs internal code changed to suit.

Martin

Did you test your 664's later? Are they really faulty? Could very well be, these prescalers seem to break quite often, if I can believe Google. Can't find a datasheet for 664 and 264 yet... I'm just reporting my machine has a 664, and it worked fine.

rick

I haven't tried the U664Bs in other circuits and I haven't looked much into the technical details but
the U664Bs are probably not faulty, it's just a different IC, functioning as intended but not quite
right for the given task for reason(s) unknown to me.

The problem is the same - only far more common - in Beomaster 6000, where the IC sits in a
warmer area, right up against a voltage regulator.
There's not a lot of room in there, but I like to bend the regulator away from the prescaler IC as much
as possible for the same reason.

I have replaced three or four prescaler ICs in Beomaster 8000s and lost count of the ones
in Beomaster 6000s - but literally dozens, perhaps a hundred.

I have seen one single U664B that seemed to be factory mounted (and replaced it because it had stopped
working), it was in a Beomaster 6000 on my bench recently. I have also heard about a few other repairers that had "luck"
with U664Bs but far more had problems like I.

The original TFK (Telefunken) U264Bs works every time in both Beomasters and I've supplied ICs to
several DIY'ers that had problems finding a replacement that worked.
(Other brands U264Bs cannot be guaranteed to work either).

Martin

Dillen wrote:

U664Bs vs U264Bs

Interesting, and thanks for the explanation!

Regarding heat: the power board of my Beomaster 8000 looks quite "fried", the area of the board between the two power resistors is quite darkened (is that normal?):

I resoldered R56 and R55 to hover about a millimeter above the board; they were touching the board before!

It must mean the board above this (the processor board) is at an elevated temperature too, although the metal shielding there may have helped to prevent damage.

rick

Your board looks slightly more cooked than average.
But it's not uncommon to see it like this.

Martin

Datasheet for u264b: link

For u664b:

Hi,

For the record, I have a 664 in my BM 6000.

Well, today I replaced the HEF40106 and the two CD4013's. The HEF40106 cost me a bicycle ride twice, because the shop was out of HEF40106's, and I only later realized that the 74HC(T)14 is a direct replacement here (5V Vss). They did have the 74HC14.

But, still: nope.

I unsocketed the 6500 master, as there are solder points under that, to see if there are any VIAs left to resolder there. But, the socket is not open, so I cannot get at the board there! Resocketed the 6500, and the board still "works" as before, so I have not damaged anything as far as I can see.

I'm a bit out of ideas at the moment. I'll do some more schematics reading, and see if that inspires any further actions.

rick *eyes the Arduino on his desk*

I have had four or five cases similar to yours.
All unresponsive in some way or another and all had to do with the 5V supply in some way. Voltage, ripple, bad filtering...
That the problem gets worse within the first minute or so as things "warm up" is also in my notes.

And thanks Jacques.

Martin

Thanks Martin!

I now notice the Display circuit has a connection to RESET, and also ST-BY to the processors, but I don't understand yet what is happening there. I could replace C3 (small 4µ7 tantalum), and even C7 (Vss elco, 10µ) just as a trial. Those circuits are not fed by the 5V but by the 12V I think..

Things that take some time to fail (that warm up minute) smell like capacitor trouble to me.

rick